Pre-cats under the turbo's.. what do they look like ?? (ie, I'm checking if Canuck S4's have em)

They are canister shaped approx. 3.5" diameter and 4"long, directly behind turbo under ...
 

thin metal heatshield. Do you see them?<p>'00 Silver S4
APR 1.0 bar
Custom downpipes and exhaust.

They are the lumps on the left of these downpipes, one still has the shield on.
 

<center><img src="http://www.imola.org/images/Dcp00062.jpg"></center><p>

How come both sets of o2 sensors come before their respective cats?
 

I'm confused. Looks like the S4 before-pre-cat and before-main-cat sensor placement could be used to measure pre-cat efficiency only.

Could someone point me to an o2 sensor tutorial that would explain o2 sensor placement reasoning?

Any guesses of how the o2 sensors are silenced in the ECU?

Jim, did you remove the pre-cat o2 sensors completely from the wiring harness?

/dan

All O2 sensors are still used in the MTM downpipes, the first pair is in the same place, just after
 

the turbos, and the second pair are installed AFTER the new sport cats (cables _barely_ long enough with re-routing!).